Expression of the IAP protein family acts cooperatively to predict prognosis in human bladder cancer patients

Abstract

The inhibitors of apoptosis (IAPs) are a group of anti-apoptotic factors in the apoptotic pathway that render cancer cells insensitive to apoptotic stimulation. Recently, several members of the IAP family have been investigated in the context of bladder cancer, and some of these have been associated with specific clinical and pathological tumor features, and with prognosis. These data suggested that the expression of an individual nuclear IAP has an important relationship with the progression of bladder cancer. To date, there are no studies concerning the overall tendencies of IAPs and their comparative therapeutic values in bladder cancer. In this study, we investigated the overall expression trends of the five tumor-related proteins, Survivin, cIAP1, cIAP2, XIAP and Livin, in normal bladder tissues and bladder cancer tissues. We classified and compared the gene expression data of these IAPs with the corresponding clinical and pathological tumor features, and with prognosis, in the development and progression of bladder cancer. The differences in IAP expression levels between archival bladder specimens from 36 normal controls and 105 patients who underwent surgery at our facility were examined using western blot analysis. The localization and expression level of each protein in low- and high-grade bladder cancer tissues were examined through immunohistochemistry. The cytoplasmic expression levels of each protein were scored as 0 (negative), +1 (weak), +2 (medium) or +3 (strong). The nuclear expression levels of cIAP1 and Survivin were scored as 0 (0%), +1 (1-25%), +2 (26-50%) or +3 (>50%). The results demonstrated that the expression of IAPs acted cooperatively to predict prognosis in human bladder cancer patients.

Keywords: bladder cancer; cooperatively; inhibitors of apoptosis; prognosis.

Figure 1

Western blot analysis of the expression of inhibitor of apoptosis (IAP) family members in normal bladder tissue and bladder cancer tissue. N, normal bladder urothelium; B1, low-grade bladder cancer; B2, high-grade bladder cancer.

Figure 2

Immunohistochemical staining of inhibitors of apoptosis (IAPs) in representative sections from different grades of bladder cancer tissue. (A–E) Images from the same sample, same area, and same visual field showing serial slices of low-grade bladder cancer tissue. (F–J) Images from the same sample, same area and same visual field, demonstrating serial slices of high-grade bladder cancer tissue.

Figure 3

Kaplan-Meier estimates of recurrence-free survival according to the expression levels of each group of IAP family members. Significant differences are observed among the high and low combinative expression subgroups, which suggests the predictive value of the combination of IAP expression levels for bladder cancer. Log-rank test P-values are listed for each parameter. Low_{cIAP1-N+Survivin-N}=scoring 0 and +1–2; Low_{cIAP1-C+cIAP2+XIAP}=scoring 0 and +1–3; Low_{Survivin-C+Livin}=scoring 0 and +1–2; High_{cIAP1-N+Survivin-N}=scoring +3–4 and +5–6; High_{cIAP1-C+cIAP2+XIAP}=scoring +4–6 and +7–9; High_{Survivin-C+Livin=scoring} +3–4 and +5–6.

Figure 4

Linear regression plot between cIAP1-N expression and Survivin-N expression. Spearman’s analysis: r=0.55, P<0.001 (SPSS 13.0). cIAP1-N, nuclear cIAP1; Survivin-N, nuclear Survivin.